Chapter 21. Recovery Manager (RMAN)

In This Chapter

• RMAN Components

• Starting RMAN

• Performing Database Backups with RMAN

• Performing Database Restores with RMAN

• Performing Database Recovery Using RMAN

• Sample Scenarios for Using RMAN

• Useful RMAN Commands

Chapter 28, "Performing Backups and Recovery," discusses the importance of a good backup strategy. In this chapter, I will discuss the Recovery Manager (RMAN), a valuable tool provided by Oracle8 to simplify and automate the process of performing database recovery on a backup under a variety of scenarios. RMAN is available both as a command-line interface and a GUI interface (integrated with the Oracle Enterprise Manager [OEM]). I will focus on the command-line interface of RMAN and discuss the following:

• RMAN components

• Perform database backups using RMAN

• Perform database recovery using RMAN

• RMAN commands and scripts

You need to understand several terms in order to work with RMAN:

• Whole backup: A backup consisting of all the datafiles and the control file.

• Full backup: A nonincremental backup of one or more datafiles.

• Incremental backup: A backup of one or more datafiles that includes only those blocks that have changed since the last incremental backup. A level 0 incremental backup of a datafile will backup all the blocks belonging to that datafile.

• Operating system level backup: Backup of one or more datafile obtained by using operating system utilities.

• Closed backup: Backup of a complete database, or a part of it, with the database closed.

• Open backup: Backup of a complete database, or a part of it, with the database open.

RMAN has several important features that simplify the process of backup and recovery:

• It can be used to perform four levels of incremental backups.

• During backup and restore, RMAN can perform checks for block corruption so that there are no surprises during database recovery. Information about corrupt blocks detected is placed in alert logs, trace files, and data dictionary views, such as v$backup_corruption and v$copy_corruption.

• It allows the backup of archived redo logs.

• The size of a backup piece can be limited, allowing easy backups of VLDBs (Very Large Databases).

• There is no need to place the tablespaces in hot backup mode because RMAN does this for you automatically.

• Several enhancements are provided over traditional backup and recovery using scripts: automatic parallelization of backup, restore, and recovery operations; limiting the number of reads per file; multiplexing of file backups; and not generating extra redo logs during backups.

• When used with an Oracle Parallel Server configuration, it can perform load balancing while performing backups, restores, and recoveries across the clustered nodes.

• RMAN scripts can be written to automate or repeat backup and restore processes.